Tools of great variety have been ground, honed and lapped for millenia past, and great effort has been expended in attempting to put the keenest possible edges on them. Certain metals, alloys, and treated steels have been developed which are capable of taking exceptionally sharp edges but practical limits have been encountered in producing and maintaining such sharpness.
From fixed blocks of smooth abrasive stones through rotated wheels, both vertical and horizontal, man has sought to create the ultimate edge by abrading and forming from a relatively blunt edge of metal a meeting of planar surfaces at various angles to form various tools. Chisels generally contain angles of from about 45.degree., and normally a mallet is used to drive the sharpened wedge into the workpiece. Other tools have been prepared having more and more acute angles to the development of razors whose planar surfaces meet at angles of about 20.degree.. Intermediately, tools having a variety of cutting edges sharpened for graving, carving, shearing and slicing, and generally hand-operated tools having a single sharpened edge, including knives and chisels, to cutting devices having mating blade elements acting together to produce shear through compressive forces have been developed and have become standard types of cutting tools.
While excellent edges on cutting tools have been obtainable, the observant user has recognized that the original edge on the newly-made cutting tool was not perfect in its creation, and that upon use better results with greater control of detail are obtained when the professed sharp tool is subjected to honing, stropping, fretting, whetting, burnishing, polishing, buffing, abrading and grinding, which are intended to create and maintain "an ultimate edge" on the cutting surface of a specific cutting tool, be it a razor, knife, chisel or graving tool. The expression "refining an edge" evolved to describe the process for obtaining and maintaining the "ultimate edge" of the cutting tool and particularly for such tools as are adapted to the highest order of skill in their ultimate use, such as for use in creating works of art and for surgical procedures.
One common type of sharpening device includes hand grinders characterized by a vertical ceramic abrasive wheel of relatively narrow width to diameter powered by a hand crank, most often operating through a gear train where one revolution of the crank produces perhaps 10 to 20 revolutions of the vertical wheel, sometimes cooled by water dropping on the surface, or the wheel moving through a water bath.
An obvious development to avoid the distraction of doing two things at once is applying a power source to replace the crank. Here, cooling, may be altered by a variety of means, mostly dependent upon water continuously extracting heat from the workpiece-wheel surface contact area. In both modifications, the abrasive surface rotates at a high rate of speed and at best their suitability is in original formation of an edge which is to be refined by means of a second process.
Power-operated devices also are available generally having a coarse grinding wheel (less than 100 grit) operating at about 3600 rpm. and a slow speed fine grit water-cooled wheel whose rpm. is substantially reduced in shear rate with the workpiece. The latter, however, is still too fast to permit "feel" in the hands of the craftsman-operator essential to a consistent approach to "refining an edge".
A present-day approach to the problem of obtaining precision sharpening are the motorized waterstones originating from Japan. In these sharpening units, there are a plurality of doughnut-like flat surface abrasive stones demountably attached in a motorized frame rotated at about 500 rpm with a working surface displaced radially outwardly from a vertical driving shaft. The abrasive surfaces allow release of the fine grit into the water which continuously flows from the stone supporting center outwardly over the motor driven grinding area. A flat planar grind is significantly less scarified by the abrasive action and the skill required demands some experience on the part of the operator. Ancillary supporting elements are often used in the combination.
In all of the above sharpening devices there is aggressive use of the metal and initial costs of the bench equipment are relatively greater than would appear required in view of the advances herein disclosed and claimed.
When examined under high magnification, even apparently very sharp tool edges are observed in actuality to be quite irregular and serrated. Also, a very common problem encountered in attempting to produce ultra sharp edges is the production of the well-known "wire edge", where a thin elongated strip of metal adheres to the sharpened edge. In conventinal practice, such "wire edge" is simply scraped away or the blade is resharpened at a less acute angle; in either event, the resultant edge is appreciably less sharp than the ideal. Consequently, many manufacturing operations employing cutting tools are less efficient than they otherwise might be, and even certain manual operations such as wood carving are rendered more difficult and frustrating.
There is also an increasing demand for the production of exceptionally flat and smooth micro surfaces and the shaping of articles to ultra precise dimensions, as in the lapping of quartz wafers in the production of frequency control devices and the lapping of single crystal silicon wafers in the production of micro circuits. It is important to reduce production costs and the percentage of rejects in these areas.
Abrasive polishing tools (wheels) have been described in the art which are flexible and deform under modest pressure. Polishing wheels generally are used on a surface which already has been brought to a specification dimension since polishing wheels are not intended to remove stock. One type of abrasive polishing wheel exhibiting the desired flexibility and deformity under mild pressures is described in U.S. Pat. No. 4,128,972. Such wheels have a "Shore A" hardness of less than 96 and comprise an abrasive grain, an elastomer bond, an inert filler and less than 10 percent by volume of voids. The relative volume amount of grain, elastomer and filler are critical to the properties and performance of the polishing wheels. Although such wheels as described in U.S. Pat. No. 4,128,972 perform as well as polishing tools, they are too soft to perform satisfactory as in honing, stropping and lapping operations.